The goal of this work is to develop an in vitro assay for ATP-driven transport systems in bacteria. Two ATP-driven potassium (K ion) transport systems of Escherichia coli will be used, both of which have high maximum rates. Since the evidence is that high energy phosphate is needed to drive these systems, they should have an assoicated phosphatase activity in vitro. Using various mutants to overcome features which may make detection of in vitro activity difficult, we will search for K ion stimulated phosphatase in crude cell extracts. The known affinities of the systems for K ion and mutants defective in the transport systems will be used to demonstrate that the stimulation is due to the presence of a K ion transport system. Once established, we will determine the components needed to demonstrate such phosphatase activity, determine the nature of the ultimate phosphate donor (which may be a compound other than ATP), and use the assay to direct purification and analysis of the transport system.